In an image forming apparatus using electrophotography, a toner image formed on a photoreceptor is transferred to paper at a transfer portion. The paper with a toner image transferred thereon is conveyed to a fixing portion and heated and pressed in this fixing portion, whereby the toner image is fixed to the paper. Thereafter, the paper is discharged from a paper discharge portion to a paper output tray and sheets of paper are stacked on the paper output tray.
However, if the paper is discharged as it is without being cooled, the sheets of paper stacked on the paper output tray are not cooled sufficiently, so that there occurs a phenomenon that the facing surfaces of the sheets stacked on the paper output tray are made to stick to each other by the toner (which will be referred to hereinbelow as a sticking phenomenon) because the paper is high in temperature. This sticking phenomenon is markedly conspicuous in duplex printing, fast printing and printing using a low melting point toner.
In order to alleviate this sticking phenomenon, there is a method whereby the length of the conveying path from the fixing portion to the paper output tray is made long so as to gain time for cooling. However, with recent development for miniaturization of image forming apparatuses, this method has become unable to be adopted.
For this reason, a scheme is adopted in which the paper after passage of the fixing portion is cooled by blowing air while it is being conveyed by pairs of conveying rollers in the conveying path. In the image forming apparatuses described in patent document 1 and patent document 2, air blowing on the paper being conveyed and exhaustion of blown air from the conveying path are carried out in the duplex printing paper path or in the paper path directly after fixing.